Radiosurgical Dose Selection for Brain Metastasis

Dose selection for brain metastasis radiosurgery is based largely upon clinical data obtained over a half century of radiosurgical treatments for various benign and malignant conditions. It is expected that within the entire radiosurgical process, the step of dose selection will occur within a framework of accurate calibration of dose delivery and accurate and detailed imaging for planning the radiosurgical treatment. Brain metastasis radiosurgery should seek lifelong, uncomplicated control. A low radiosurgery dose that will not control the tumor will not achieve this therapeutic goal, and neither will a radiosurgery dose that controls the tumor but causes symptomatic brain radiation necrosis. The volume of the metastasis being targeted and the volume of normal tissues receiving substantial radiosurgical doses are of paramount importance in dose selection. A high degree of conformality of the high-dose radiosurgical treatment volume to the metastasis has been shown to decrease complications, as does a steep dose gradient between the metastasis and adjacent normal brain tissue. A dose-escalation trial conducted by the Radiation Therapy Oncology Group that differentially dose-escalated radiosurgical doses for tumors of different sizes established that single-fraction doses between 15 and 24 Gy are relatively safe in patients who have received prior fractionated radiation therapy to the brain. Corresponding data do not exist for patients who are treated with primary radiosurgery and no whole brain radiation therapy. A dose-escalation trial for three-fraction radiosurgical treatment of brain metastases is being conducted at Stanford. Knowledge of prior whole brain radiation therapy treatment details, including the dose delivered and the time interval since that treatment was given may affect the choice of radiosurgical dose, as may recent administration of systemic, radiation-potentiating chemotherapy. Physician knowledge and careful judgment, together with careful treatment planning and delivery can minimize the risks associated with brain metastasis radiosurgery.